Many industrial and consumer articles, e.g. machine parts, vehicle bodies, furniture and sporting equipment, are spray painted in enclosed areas called paint spray booths. Generally a significant portion of the paint is oversprayed, that is, not transferred to the object being coated. Such waste paint is generally referred to as oversprayed paint. The purposes of paint spray booths are to contain any fumes or paint overspray, reduce the risk of contamination of the article being painted and protect the health of the workers at the site. Smaller booths may employ filters to remove the paint overspray from the air, but larger systems usually use a recirculating water system for this purpose. Paint spray booths utilizing a recirculating water system are generally comprised of a spraying chamber, a duct system for passing an air stream down through the chamber, and a water system including a sump and a number of pipes, pumps, meters and valves. Airflow through the chamber forces the paint overspray into contact with the resident water in the sump, thereby transferring the paint from the air into the water. The result is the oversprayed paint contacts and is captured by the recirculating water of the spray booth.
During paint spray booth use, significant concentrations of paint can build up in the water system. Non-water-based paint, e.g. organic solvent-based paint, tends to remain tacky in the water system and can plug pipes, pumps meters & valves, as well as coat the inside of the sump, eventually forming a difficult to remove and hazardous sludge. Paint sludge is a known medium for microbial growth, which is a health and environmental concern during use of the system and in the removal and disposal of the sludge. It is desirable to reduce the microbial growth by preventing paint deposits in the recirculating water system, including at the bottom of the sump.
Both water-based and non-water-based paint accumulate in the recirculating water of the system, unless the paint is removed. Paint that is water-based generally disperses in the recirculating water system without detackification. Over time, use of either type of paint in a booth results in paint-saturated water that is progressively less effective in its air scrubbing action. The paint-saturated water must either be replaced or treated to remove accumulated paint. Replacement and disposal of resident water that is paint-saturated is uneconomical and raises environmental concerns, thus treatment of the water is preferred.
In order to render the paint more readily removable from the water, to preserve its air cleaning action, water in the sump is generally treated so that the oversprayed paint, when it is brought into contact with such water, forms paint sludge. Paint sludge typically floats at or near the surface of the sump water or sinks. Paint sludge that sinks is generally removed by draining the water and shoveling or scraping the sludge out of the sump, which increases expensive downtime for the paint booth. For ease of removal, it is preferred that as much as possible of the paint sludge formed is of the floating variety, which can be removed by skimming or similar means. Removal of floating paint sludge can be a continuous or non-continuous process and is useful in reducing downtime of the paint booth. The tendency of such paint sludge to float also permits reasonably efficient water recycling, because relatively sludge-free water can be drawn from near the bottom of the sump.
It is important to the efficient operation of paint spray booths, and to the efficient waste treatment of such oversprayed paint wastes, that the oversprayed paint be detackified when it contacts the water system. Typically, solvent-based paint requires detackification, flocculation and flotation for removal, while water-based paint usually requires only flocculation and flotation. By detackification is meant herein that the adhesive properties (tackiness) of the paint overspray are minimized or eliminated. It is undesirable to have such paint overspray adhere to any surface that may be encountered in the spray booth, or during its removal from the spray booth and subsequent disposal.
It is also advantageous if a paint detackifying agent promotes the formation of paint sludge that can be efficiently removed and dewatered. Ideally, the detackifying agent also acts as a flocculent. Removal and dewatering of paint sludge is affected by a plurality of sludge characteristics, including besides detackification, cohesiveness to promote easy sludge removal, low water content for total volume reduction, low or no solvent encapsulation to reduce the hazardous properties of the sludge, particle or agglomerate size of floating sludge and the like. High solids and minimum solvent are requirements under most sludge landfill disposal regulations. An initial dewatering of the sludge occurs during sludge removal, and the sludge collected may be further dewatered using such devices as a plate and frame filter, a vacuum filter, a centrifuge, a twin belt press or the like. For effective dewatering during sludge removal, and when the collected sludge is further dewatered using a dewatering device, the sludge paint must be well detackified.
Chemicals for detackifying paint and chemicals for flocculating paint are known in the industry. Generally, detackifying chemicals in the paint booth water system cause changes in the surface characteristics of paint droplets captured in the water system rendering them less sticky or tacky. Reducing the tackiness of the paint droplets reduces the deposition of the captured paint on reservoir surfaces and piping portions of the paint booth water system.
Detackifiers allow captured paint to be dispersed in the water system, but often do not facilitate the paint's removal from the water system. Some detackifiers of the prior art tend to render paint in the water as fine dispersion that is not readily removable. It is desirable that the detackified paint be easily removable from the water system, without costly and time-consuming shutdowns for cleaning of the sump and piping and disposal of the wash water. One means of rendering the paint readily removable is the introduction of additives such as flocculents that cause the detackified paint to aggregate into small clumps that can then be removed from the water.
Examples of commercial detackification chemicals include melamine formaldehyde solutions, such as those taught in U.S. Pat. No. 5,599,884, incorporated herein by reference. Melamine formaldehyde products have the drawback of requiring a flocculent to cause adequate agglomeration of the detackified paint for removal. The functioning of known melamine formaldehyde products is also pH sensitive, requiring pH adjustment to maintain effectiveness. Too high pH results in undesirable foaming of the resident water, while too low pH results in poor detackfication performance. Flocculents are provided in a separate package, as is an alkali for pH control. The three-package system, of detackifier, flocculent and alkali is generally added at different locations in the system. This multiple additive product is inconvenient and has the potential for introducing error by use of incorrect proportions of the separate parts.
Other known products that detackify and flocculate paint in the prior art include compositions based upon clay. One standard definition for the term “clay” is that of a “naturally occurring sediment (including that obtained by alteration in situ by supergene and hydrothermal processes) or sedimentary rock composed of one or more minerals and accessory compounds, the whole usually being rich in hydrated silicates of aluminum, iron or magnesium, hydrated alumina, or iron oxide, predominating in particles of colloidal or near-colloidal size, and commonly developing plasticity when sufficiently pulverized and wetted.” Kirk-Othmer, Encyclopedia of Chemical Technology, Volume 5, page 544, (2nd edition) John Wiley and Sons, Inc., New York, N.Y. 1964.
U.S. Pat. No. 4,629,572 discloses the use of condensation resins of aldehyde and nitrogeneous compounds such as urea, melamine, thiourea, dicyanadiamide, substituted melamine and others in combination with clay. The two additives are charged separately to the circulating water to avoid coagulation of these components. The resin used in this detackifier is not cured to the extent that it forms an insoluble and infusible product. Like the clay flocculent, the resin is used in the form of a colloidal suspension.
The clay-based systems are capable of detackifying and flocculating paints, but have the drawback of substantially increasing the turbidity of the treated water. The increased turbidity is evidence of the presence of a substantial amount of colloidal particles remaining in the treatment water. This gives the treatment water an unappealing cloudy appearance. Further, in use, the water treatment system tends to build up increasing amounts of the colloidal material as more clay treatment is added to the system. Over time, this build-up negatively affects the water system's air scrubbing efficiency. A treatment or additive for paint booth water that avoids this drawback is desirable.
It is also desirable that the additive be dispersible in the paint booth water system with reasonable efficiency. An additive that requires auxiliary equipment for dispersing, requires separate measurement and addition of individual components or requires separate addition times and locations would increase the operation costs and service time required. Hence, it is desirable that the additive can be provided in suitable form to be added as a single charge directly to the water system, and be dispersed homogeneously therein rapidly, at normal operating temperatures and without agitation other than that provided by the normal operation pumping action and the like.
As noted above, it is preferable that the paint sludge formed floats on or near the top of the water present in the sump. Sinking sludge requires shutdown of the paint booth for periodic cleaning and sludge removal, which adds cost. Generating such floating sludge, and reducing the amount of sinking sludge, is desirable and extends the time between sump cleanings. Generation of floating sludge in some systems is assisted by air flotation means. The removal of the sludge on or near the top of the water may be accomplished using one or more of a variety of systems, including without limitation by skimming, by screening of straining, by dispersing the sludge in the water of the system and then discharging a portion of such water, and the like. In some operations, the sludge removal is continuous and such continuous sludge removal systems frequently use a pedal wheel, skimmer, or a side-stream sludge removal when an air assisted floating unit is used to separate the sludge from the water. As noted above, efficient sludge removal is dependent in part on sludge characteristics. The paint should be well detackified and the sludge preferably should be cohesive.
There is a need for a product that both detackifies and flocculates paint without additional ingredients, while providing improved water clarity and facilitating paint and paint sludge removal. There is also a need for a easy means for treating paint booth water systems, for example by eliminating multiple packages, measurement of multiple ingredients, different addition locations, and frequent pH monitoring and adjustment.
Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word “about” in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless expressly stated to the contrary: percent, “parts of”, and ratio values are by weight or mass; the term “polymer” includes oligomer, copolymer, terpolymer and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counter ions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counter ions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counter ions may be freely selected, except for avoiding counter ions that act adversely to an object of the invention; the word “mole” means “gram mole”, and the word itself and all of its grammatical variations may be used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; the term The terms “solution”, “soluble”, “homogeneous”, and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18–25° C. The term “paint” as used herein includes paint in its ordinary sense, that is, a mixture of pigment and a suitable liquid vehicle that is reasonably fluid and provides a thin and adherent coating when spread on an appropriate surface. The term “paint” as used herein also includes other paint-like fluid coating materials. Hence, the term “paint” as used herein refers to paints, lacquers, varnishes, base coats, clear coats and the like.